Beer Fermentation Tanks: Difference between revisions

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===Do the microbes change their environment?===
===Do the microbes change their environment?===
Do they alter pH, attach to surfaces, secrete anything, etc. etc.
From a human standpoint, the whole point of using yeast for beer fermentation is to transform the sugars within the wort into ethanol and other flavor changing molecules.  The preparation of the environment is as follows: the wort is prepared by boiling and quick chilling used to help coagulate excess protein for removal.  Also by dropping the temperature to optimum growth range, premature fermentation is prevented.  Once out of the lag phase, the yeast reaches the growth phase where it uses aerobic respiration until all the oxygen is removed from the environment.  While in respiration phase, the yeast oxidizes acid compounds, dropping pH of the environment.  The oxygen is used up during respiration and the carbon dioxide produced by the yeast also helps to remove any traces of oxygen, called “scrubbing”.  Now the yeast switches to anaerobic respiration: fermentation.  During fermentation the simple sugars are converted to ethanol and carbon dioxide.  In lagers however, unlike ales, the presence of esters (fruity flavors) and diacetyl (butterscotch-like flavors) is considered a flaw.  Due to the low temperatures at which S. pastorianus ferments, a naturally lower amount of esters and diacetyl is produced.  The low temperature is also the cause for the production of sulfur compounds which is gradually incorporated and gives the lager the clean, crisp taste.  Once completed, the wort will have lowered simple sugar content, elevated ethanol content, carbon dioxide, sulfer compounds, and lowered pH and specific gravity.  [http://byo.com/feature/538.html (4)]


===Do the microbes carry out any metabolism that affects their environment?===
===Do the microbes carry out any metabolism that affects their environment?===

Revision as of 22:17, 26 August 2008

Description of Niche

Where located?

Physical Conditions?

What are the conditions in your niche? Temperature, pressure, pH, moisture, etc.

Influence by Adjacent Communities (if any)

Is your niche close to another niche or influenced by another community of organisms?

Conditions under which the environment changes

Do any of the physical conditions change? Are there chemicals, other organisms, nutrients, etc. that might change the community of your niche.

Who lives there?

Ale Fermenting Yeast

Which microbes are present?

You may refer to organisms by genus or by genus and species, depending upon how detailed the your information might be. If there is already a microbewiki page describing that organism, make a link to it.

Are there any other non-microbes present?

Plants? Animals? Fungi? etc.

Do the microbes that are present interact with each other?

Describe any negative (competition) or positive (symbiosis) behavior

Do the microbes change their environment?

Do they alter pH, attach to surfaces, secrete anything, etc. etc.

Do the microbes carry out any metabolism that affects their environment?

Do they ferment sugars to produce acid, break down large molecules, fix nitrogen, etc. etc.

Lager Fermenting Yeast

Which microbes are present?

Ideally during the fermentation step in beer brewing, the only microbe present is the specific strain of yeast that the brewer uses. The most common yeast used for brewing lager is Saccharomyces pastorianus (also called Saccharomyces carlsbergensis) (1). These are cold, bottom fermenting yeast (as opposed to the top fermenting yeast for ales). They ferment in a temperature range of 7-15°C (45-59°F) (2). Because of the lower range they ferment at a slower rate, resulting in less foam and thus when the yeast flocculates, it settles to the bottom of the tank.

Are there any other non-microbes present?

There are no non-microbes living in a beer fermentation vat (preferably).

Do the microbes that are present interact with each other?

S. pastorianus naturally ferments for a longer time than ale yeasts which calls for the necessity of careful sanitization of the vat and area as to avoid contamination by wild microbes. Due to the presence of only a single population of yeast, microbe interaction is limited to how the yeast within the population grow. One very important trait of yeast for brewers is that at certain conditions, yeast flocculates. The conditions are ideally when the sugars within the wort have been converted to ethanol and available energy sources are low. Flocculation is the aggregation of yeast cells into clumps that sediment in the environment. With S. pastorianus, these clumps sink to the bottom of the tank, hence the name bottom-fermenting yeast. In brewing yeast, this is an asexual aggregation where the yeast prepares for dormancy by producing glycogen: the microbe’s preparation at the end of the stationary phase caused by starvation. In S. pastorianus, flocculation is controlled by a lectin-mediated mechanism and requires Ca+. Lectin is recognized by mannan receptors on yeast cells, and so the presence of mannose blocks this mechanism. Unlike with ale yeasts, flocculation of S. pastorianus, is not affected by the pH of the environment. (3)

Do the microbes change their environment?

From a human standpoint, the whole point of using yeast for beer fermentation is to transform the sugars within the wort into ethanol and other flavor changing molecules. The preparation of the environment is as follows: the wort is prepared by boiling and quick chilling used to help coagulate excess protein for removal. Also by dropping the temperature to optimum growth range, premature fermentation is prevented. Once out of the lag phase, the yeast reaches the growth phase where it uses aerobic respiration until all the oxygen is removed from the environment. While in respiration phase, the yeast oxidizes acid compounds, dropping pH of the environment. The oxygen is used up during respiration and the carbon dioxide produced by the yeast also helps to remove any traces of oxygen, called “scrubbing”. Now the yeast switches to anaerobic respiration: fermentation. During fermentation the simple sugars are converted to ethanol and carbon dioxide. In lagers however, unlike ales, the presence of esters (fruity flavors) and diacetyl (butterscotch-like flavors) is considered a flaw. Due to the low temperatures at which S. pastorianus ferments, a naturally lower amount of esters and diacetyl is produced. The low temperature is also the cause for the production of sulfur compounds which is gradually incorporated and gives the lager the clean, crisp taste. Once completed, the wort will have lowered simple sugar content, elevated ethanol content, carbon dioxide, sulfer compounds, and lowered pH and specific gravity. (4)

Do the microbes carry out any metabolism that affects their environment?

Do they ferment sugars to produce acid, break down large molecules, fix nitrogen, etc. etc.

Current Research

Enter summaries of the most recent research. You may find it more appropriate to include this as a subsection under several of your other sections rather than separately here at the end. You should include at least FOUR topics of research and summarize each in terms of the question being asked, the results so far, and the topics for future study. (more will be expected from larger groups than from smaller groups)

References

[Sample reference] Takai, K., Sugai, A., Itoh, T., and Horikoshi, K. "Palaeococcus ferrophilus gen. nov., sp. nov., a barophilic, hyperthermophilic archaeon from a deep-sea hydrothermal vent chimney". International Journal of Systematic and Evolutionary Microbiology. 2000. Volume 50. p. 489-500.

1. “Saccharomyces pastorianus”. Wikipedia. 7 August 2008.

2. Goldammer, Ted. “The Brewers’ Handbook, The Complete Book to Brewing Beer”. December 2000. Chapter 4.

3. Dengis, Pascale B., L. R. Nélissen, and Paul G. Rouxhet. “Mechanisms of Yeast Flocculation: Comparison of Top- and Bottom-Fermenting Strains”. Applied and Environmental Microbiology. February 1995. Pages 718-728.

4. Oliver, John. “10 Keys to Great Lager”. Brew your own: The How-to Homebrew beer magazine. September 1999.

5. “Diacetyl”. Wikipedia. 16 August 2008.

6. “Laagering FAQs”. Midwest: Homebrewing & Winemaking Supplies. 2005

Edited by Daniel Stromwall, Andrea Lin, and Chrissta Maracle; students of Rachel Larsen